Pollution Control in the Wood Preserving Industry. Part IV. Biological Methods of Treating Wastewater

The oxidation efficiency of pollutants in effluents from creosote treatments was studied using activated-sludge, trickling-filter, and soil-percolation processes. Design criteria based on the results obtained are presented. In a related study, the biodegradability of pentachlorophenol was investigated. Substrate removals in bench-scale, activated-sludge units under steady-state conditions averaged 60, 77, 82, and 85 percent for detention times of 5, 10, 15, and 20 days, respectively. The reaction rate constant and rate of oxygen utilization calculated from the results are discussed in relation to their use in design applications. Optimum conditions for BOB removal were reached in a pilot trickling filter with a recirculation rate of 14 to 1 and loading rate of 66 lbs./1,000 ft.3 per day. Removal efficiency at this loading was 92 Percent. The comparable value for phenols at a loading rate of 1.2 lbs./1,000 ft.3 per day was 97 percent. The most promising results were obtained in pilot-scale tests of soil Percolation. Reduction in COD, based on the raw waste delivered to the percolation field, were 95, 95, and 97 percent at soil depths of 1, 2, and 4 feet, respectively. Comparable values for phenols at the same depths were, in order, 98.9, 99.2, and 99.6 percent. Laboratory studies of this method of waste treatment indicated that the optimum loading rate is 3500 gallons per acre per day. The performance of activated-sludge units used to treat pentachlorophenol wastewater was quite variable and was not related to detention time. Units inoculated with sludge from a municipal sewage treatment plant were the most variable, the removal rate generally decreasing with time during the study from an initial value of about 86 percent to a final value of 23 percent. Units inoculated with cultures prepared from soil collecting at a treating plant consistently removed in excess of 90 percent of the pentachlorophenol added, and one unit was removing in excess of 97 percent when the study was terminated.

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